Thin film transistor substrate and display using the same

ABSTRACT

Provided are a thin film transistor (TFT) substrate and a display using the same. A TFT substrate includes: a substrate, a first TFT on the substrate, including: a polycrystalline semiconductor layer, a first gate electrode thereover, a first source electrode, and a first drain electrode, a second TFT on the substrate, including: a second gate electrode, an oxide semiconductor layer on the second gate electrode, a second source electrode, and a second drain electrode, an intermediate insulating layer including a nitride layer, on the first gate electrode, and an oxide layer covering the second gate electrode, on the intermediate insulating layer, on the oxide layer, and overlapping the second gate electrode, wherein the first source, first drain, and second gate electrodes are between the intermediate insulating layer and the oxide layer, and wherein the second source and the second drain electrodes are on the oxide semiconductor layer.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims the benefit of U.S. Provisional Application No.61/943,628, filed on Feb. 24, 2014, the entire disclosure of which ishereby incorporated by reference herein for all purposes.

BACKGROUND

1. Technical Field

The present disclosure relates to a thin film transistor substratehaving two different types of thin film transistors on the samesubstrate, and a display using the same.

2. Discussion of the Related Art

Nowadays, as the information society is developed, the requirements ofdisplays for representing information are increasing. Accordingly,various flat panel displays (FPDs) are developed for overcoming manydrawbacks of the cathode ray tube (CRT) such as heavy weight and bulkvolume. Flat panel display devices include a liquid crystal displaydevice (LCD), a plasma display panel (PDP), a organic light emittingdisplay device (OLED), and a electrophoresis display device (ED).

The display panel of a flat panel display may include a thin filmtransistor substrate having a thin film transistor allocated in eachpixel region arrayed in a matrix manner. For example, the liquid crystaldisplay device (LCD) represents video data by controlling the lighttransitivity of the liquid crystal layer using electric fields. Theorganic light emitting diode display represents video data by generatingproperly controlled light at each pixel disposed in a matrix mannerusing an organic light emitting diode formed in each pixel.

As a self-emitting display device, the organic light emitting diodedisplay device has merits including very fast response speed, highbrightness, and large viewing angle. The organic light emitting diodedisplay (OLED) using the organic light emitting diode having good energyefficiency can be categorized in the passive matrix type organic lightemitting diode display (PMOLED) and the active matrix type organic lightemitting diode display (AMOLED).

As personal appliances have been more adopted, portable and/or wearabledevices have been actively developed. To apply the display device for aportable and/or wearable device, the device should have low powerconsumption. However, using already developed technologies, a limitationhas been getting a display with low power consumption.

SUMMARY

Accordingly, the present invention is directed to a thin film transistorsubstrate and display using the same that substantially obviate one ormore of the problems due to limitations and disadvantages of the relatedart.

An object of the present invention is to provide a thin film transistorsubstrate for a flat panel display having at least two transistorshaving different characteristics from each other on the same substrate.

Another object of the present invention is to provide a thin filmtransistor substrate for a flat panel display having two different typesof transistors manufactured with an efficient manufacturing process andreduced number of mask processes.

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention. Theobjectives and other advantages of the invention will be realized andattained by the structure particularly pointed out in the writtendescription and claims hereof as well as the appended drawings.

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described, a thin filmtransistor substrate includes: a substrate, a first thin film transistordisposed on the substrate, the first thin film transistor including: apolycrystalline semiconductor layer, a first gate electrode over thepolycrystalline semiconductor layer, a first source electrode, and afirst drain electrode, a second thin film transistor disposed on thesubstrate, the second thin film transistor including: a second gateelectrode, an oxide semiconductor layer on the second gate electrode, asecond source electrode, and a second drain electrode, an intermediateinsulating layer including a nitride layer and disposed on the firstgate electrode, and an oxide layer covering the second gate electrodeand disposed on the intermediate insulating layer, wherein the oxidesemiconductor layer is disposed on the oxide layer and overlaps thesecond gate electrode, wherein the first source electrode, the firstdrain electrode, and the second gate electrode are disposed between theintermediate insulating layer and the oxide layer, and wherein thesecond source electrode and the second drain electrode are disposed onthe oxide semiconductor layer.

In another aspect, a thin film transistor substrate includes: asubstrate; a first semiconductor layer disposed on the substrate, thefirst semiconductor layer comprising a polycrystalline semiconductormaterial; a gate insulating layer covering the first semiconductorlayer; a first gate electrode disposed on the gate insulating layer, thefirst gate electrode overlapping the first semiconductor layer; anintermediate insulating layer comprising a nitride layer, theintermediate insulating layer covering the first gate electrode; asecond gate electrode, a first source electrode, and a first drainelectrode disposed on the intermediate insulating layer; an oxide layercovering: the first source electrode; the first drain electrode; and thesecond gate electrode; a second semiconductor layer comprising an oxidesemiconductor material disposed on the oxide layer, the secondsemiconductor layer overlapping the second gate electrode; and a secondsource electrode and a second drain electrode disposed on the secondsemiconductor layer.

Other systems, methods, features and advantages will be, or will become,apparent to one with skill in the art upon examination of the followingfigures and detailed description. It is intended that all suchadditional systems, methods, features and advantages be included withinthis description, be within the scope of the present disclosure, and beprotected by the following claims. Nothing in this section should betaken as a limitation on those claims. Further aspects and advantagesare discussed below in conjunction with the embodiments. It is to beunderstood that both the foregoing general description and the followingdetailed description of the present disclosure are examples andexplanatory, and are intended to provide further explanation of thedisclosure as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate implementations of the inventionand together with the description serve to explain the principles of theinvention.

FIG. 1A is a cross sectional view illustrating a structure of a thinfilm transistor substrate for a flat panel display in which twodifferent type thin film transistors are formed according to anembodiment.

FIG. 1B is a cross sectional view illustrating a structure forconnecting between the data line and source electrode, and between thegate line and the gate electrode in the thin film transistor shown inFIG. 1A.

FIG. 2 is a flow chart illustrating a method for manufacturing the thinfilm transistor substrate for a flat panel display in which twodifferent type thin film transistors are formed according to anembodiment.

FIG. 3 is a cross sectional view illustrating a structure of a thin filmtransistor substrate for a flat panel display in which two differenttype thin film transistors are formed according to an embodiment.

FIG. 4 is a flow chart illustrating a method for manufacturing the thinfilm transistor substrate for a flat panel display in which twodifferent type thin film transistors are formed according to anembodiment.

FIG. 5 is a cross sectional view illustrating a structure of a thin filmtransistor substrate for a flat panel display in which two differenttype thin film transistors are formed according to an embodiment.

FIG. 6 is a flow chart illustrating a method for manufacturing the thinfilm transistor substrate for a flat panel display in which twodifferent type thin film transistors are formed according to anembodiment.

FIG. 7 is a block diagram illustrating a structure of the displayaccording to an embodiment.

FIG. 8 is a plane view illustrating a thin film transistor substratehaving an oxide semiconductor layer included in a fringe field typeliquid crystal display according to an embodiment.

FIG. 9 is a cross-sectional view illustrating the structure of the thinfilm transistor substrate of FIG. 8 by cutting along the line I-I′according to an embodiment.

FIG. 10 is a plane view illustrating the structure of one pixel for theactive matrix type organic light emitting diode display having theactive switching elements such as the thin film transistors according toan embodiment.

FIG. 11 is a cross sectional view illustrating the structure of theorganic light emitting diode display along to the cutting line of II-II′in FIG. 10 according to an embodiment.

FIG. 12 is an enlarged plane view illustrating a structure of an organiclight emitting diode display according to a fourth application exampleof the present disclosure.

FIG. 13 is a cross sectional view illustrating a structure of theorganic light emitting diode display along to the cutting line ofIII-III′ in FIG. 12, according to an embodiment.

Throughout the drawings and the detailed description, unless otherwisedescribed, the same drawing reference numerals should be understood torefer to the same elements, features, and structures. The relative sizeand depiction of these elements may be exaggerated for clarity,illustration, and convenience.

DETAILED DESCRIPTION

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. Like reference numerals designate like elements throughout thedetailed description. However, the present disclosure is not restrictedby these embodiments but can be applied to various changes ormodifications without changing the technical spirit. In the followingembodiments, the names of the elements are selected for ease ofexplanation and may be different from actual names. Hereinafter, themeaning for the term of “on” includes “directly on” and “indirectly on”in all scopes of the specification. Similarly, the meaning for the termof “over” includes “directly over” and “indirectly over” in all scopesof the specification. Further, the meaning for the term of “under”includes “directly under” and “indirectly under” in all scopes of thespecification.

The thin film transistor substrate for a flat panel display according tothe present disclosure comprises a first thin film transistor disposedin a first area and a second thin film transistor disposed in a secondarea, on the same substrate. The substrate may include a display areaand a non-display area. In the display area, a plurality of pixel areais arrayed in a matrix manner. In one pixel area, the display elementsare disposed. In the non-display area surrounding the display area, thedriver elements for driving the display elements in the pixel area aredisposed.

Here, the first area may be the non-display area, and the second areamay be some portions or all portions of the display area. In this case,the first thin film transistor and the second thin film transistor aredisposed as they may be apart from each other. Otherwise, the first areaand the second area may be included in the display area. Especially, forthe case that a plurality of thin film transistor are disposed in onepixel area, the first thin film transistor and the second thin filmtransistor may be closely disposed.

As the polycrystalline semiconductor material has the characteristics ofhigh mobility (over 100 cm2/Vs) and of low energy consumption power, andit has high reliability, it is proper to apply to the driver IC, such asthe gate driver and/or the multiplexer (MUX) for driving the displayelements. In addition, it can be applied to the driving thin filmtransistor disposed in the pixel area of the organic light emittingdiode display. As the oxide semiconductor material has low off-current,it is proper to apply to the channel layer of the switching thin filmtransistor in the pixel area, in which the ON time period is very shortbut the OFF time period is long. Further, as the off-current is low, theholding time of the pixel voltage may be long, so that it is preferableto apply the display with low frequency drive and/or low powerconsumption. By disposing these two different type thin filmtransistors, the present disclosure suggests a thin film transistorsubstrate having an optimized function and characteristic for theportable and/or wearable displays.

When the semiconductor layer is formed using the polycrystallinesemiconductor material, the doping process and high temperaturetreatment process are used. On the contrary, when the semiconductorlayer is formed using the oxide semiconductor material, it is performedunder a relatively lower temperature process. Therefore, it ispreferable that the polycrystalline semiconductor layer, performed undera more severe heat condition, is first formed, and after that, the oxidesemiconductor layer is formed. To do so, in the present disclosure, thefirst thin film transistor having the polycrystalline semiconductormaterial may have a top gate structure, and the second thin filmtransistor having the oxide semiconductor material would have a bottomgate structure.

Further, in view of manufacturing process, when the polycrystallinesemiconductor material has a lot of vacancy, the characteristics may beseverely degraded. Therefore, a hydrogenation process may be performedin which the vacancies are filled with hydrogen particles. On the otherhand, for the oxide semiconductor material, the vacancies may act as thecarriers, so it may be desired that the thermal treatment be performedwith a small amount of vacancies in the oxide semiconductor material.These processes, the hydrogenation process and the thermal treatment,can be performed by a post-thermal process under a 350˜380° C.temperature condition.

For the hydrogenation process, a nitride layer having a lot of hydrogenparticles may be provided over the polycrystalline semiconductormaterial. As the materials used for depositing the nitride layer has alarge amount of hydrogen, a lot of hydrogen particles may be includedinto the deposited nitride layer. By the thermal process, the hydrogenparticles can be diffused into the polycrystalline semiconductormaterial. As the result, the polycrystalline semiconductor layer can bestabilized. During the thermal process, too much of the hydrogenparticles should not be diffused into the oxide semiconductor material.Therefore, an oxide layer should be disposed between the nitride layerand the oxide semiconductor material. As a result, the oxidesemiconductor layer can be stabilized but may be affected too much bythe hydrogen particles.

Hereinafter, for convenience, the first thin film transistor is for thedriver IC disposed in the non-display area and the second thin filmtransistor is for the display element disposed in the pixel area of thedisplay area. However, embodiments are not restricted to this case. Forexample, in a organic light emitting diode display, the first thin filmtransistor and the second thin film transistor may be disposed at onepixel area in the display area. Especially, the first thin filmtransistor having the polycrystalline semiconductor material may beapplied for the driving thin film transistor, and the second thin filmtransistor having the oxide semiconductor material may be applied forthe switching thin film transistor.

First Embodiment

FIG. 1A is a cross sectional view illustrating a structure of a thinfilm transistor substrate for a flat panel display in which twodifferent type thin film transistors are formed according to a firstembodiment of the present disclosure. FIG. 1B is a cross sectional viewillustrating a structure for connecting between the data line and sourceelectrode, and between the gate line and the gate electrode in the thinfilm transistor shown in FIG. 1A. Here, the cross sectional views moreclearly and conveniently show the main features of the presentdisclosure.

With reference to FIG. 1A, the thin film transistor substrate for a flatpanel display according to the first embodiment comprises a first thinfilm transistor T1 and a second thin film transistor T2 which aredisposed on the same substrate SUB. The first and second thin filmtransistors T1 and T2 may be far apart from each other, or they may bedisposed within a relatively close distance. Otherwise, these two thinfilm transistors are disposed as being overlapping each other.

On the whole surface of the substrate SUB, a buffer layer BUF isdeposited. In some cases, the buffer layer BUF may not be included. Or,the buffer layer BUF may be a plurality of layers. Here, forconvenience, a single layer arrangement will be explained. Further, alight shield layer may be included at some areas between the substrateSUB and the buffer layer BUF. The light shield layer may be furtherdisposed to prevent the light from inducing into the semiconductor layerof the thin film transistor disposed thereon.

On the buffer layer BUF, a first semiconductor layer A1 is disposed. Thefirst semiconductor layer A1 includes a channel area of the first thinfilm transistor T1. The channel area is defined as the overlapped areabetween the first gate electrode G1 and the first channel layer A1. Asthe first gate electrode G1 is overlapped with the middle portions ofthe first semiconductor layer A1, the middle portion of the firstsemiconductor layer A1 is the channel area. The two areas expanded toboth sides of the channel area where the impurities are doped aredefined as the source area SA and the drain area DA, respectively.

For the case that the first thin film transistor T1 is for the driverIC, it is preferable that the semiconductor layer has a characteristicfor high speed performance with a lower power consumption. For example,P-MOS type or N-MOS type thin film transistor may be used, or C-MOS typemay be applied for the first thin film transistor T1. The P-MOS, N-MOSand/or C-MOS type thin film transistor preferably has a polycrystallinesemiconductor material, such as poly-crystalline silicon (p-Si).Further, the first thin film transistor T1 preferably has a top gatestructure.

On the whole surface of the substrate SUB having the first semiconductorlayer A1, a gate insulating layer GI is deposited. The gate insulatinglayer GI may be made of the silicon nitride (SiN_(x)) material or thesilicon oxide (SiO_(x)) material. It may be preferable that the gateinsulating layer GI has the thickness of 1,000 Å ˜1,500 Å for ensuringthe stability and characteristics of the elements. In the case that thegate insulating layer GI may be made of silicon nitride (SiN_(x)), inthe view point of manufacturing process, the gate insulating layer GIincludes a lot of hydrogen particles. As these hydrogen particles wouldbe diffused out from the gate insulating layer GI, it is preferable thatthe gate insulating layer GI is made of silicon oxide material.

The diffusion of the hydrogen particles may cause positive effects onthe first semiconductor layer A1 including polycrystalline semiconductormaterial. However, it may cause negative effects on the second thin filmtransistor T2 having different material from the first thin filmtransistor T1. Therefore, when at least two thin film transistors havingdifferent characteristics from each other are formed on the samesubstrate SUB, it is preferable that the gate insulating layer GI wouldbe made of silicon oxide (SiO_(x)), which is less likely to affect thesemiconductor material. In some cases, unlike in the first embodiment,the gate insulating layer GI may be deposited as having the thickness of2,000 Å˜4,000 Å. In those cases, when the gate insulating layer GI ismade of the nitride silicon (SiN_(x)), much more of the hydrogenparticles may be diffused. Considering these cases, it is preferablethat the gate insulating layer GI would be the oxide layer, such assilicon oxide (SiO_(x)).

A first gate electrode G1 may be disposed on the gate insulating layerGI. The first gate electrode G1 may overlap the middle portion of thefirst semiconductor layer A1. The middle portion of the firstsemiconductor layer A1 overlapping with the gate electrode G1 may bedefined as the channel area.

As covering the first gate electrodes G1, an intermediate insulatinglayer ILD may be deposited on the whole surface of the substrate SUB.The intermediate insulating layer ILD may be made of a nitride layerSIN, including a silicon nitride (SiN_(x)). The nitride layer SIN may bedeposited for performing the hydrogenation process to the firstsemiconductor layer A1 having the polycrystalline silicon by diffusingthe hydrogen particles into the polycrystalline silicon.

A first source electrode S1, a first drain electrode D1, and a secondgate electrode G2 may be disposed on the intermediate insulating layerILD. The first source electrode S1 may contact the source area SA, oneportion of the first semiconductor layer A1 via the source contact holeSH penetrating the intermediate insulating layer ILD, and the gateinsulating layer GI. The first drain electrode D1 may contact the drainarea SA, another portion of the first semiconductor layer A1 via thedrain contact hole DH penetrating the intermediate insulating layer ILD,and the gate insulating layer GI. The second gate electrode G2 may bedisposed where the second thin film transistor T2 is placed. In formingthe first source electrode S1, the first drain electrode D1 and thesecond gate electrode G2 may be formed with a same material and a samemask process at the same layer, so the manufacturing process can besimplified.

An oxide layer SIO may be deposited on the intermediate insulating layerILD having the first source electrode S1, the first drain electrode D1and the second gate electrode G2. The oxide layer SIO may include aninorganic oxide material, such as a silicon oxide (SiO_(x)) material. Asthe oxide layer SIO may be stacked on the nitride layer SIN, the oxidelayer SIO may prevent the hydrogen particles of the nitride layer SINfrom being diffused too much into the semiconductor material of thesecond thin film transistor T2.

The hydrogen particles going out from the intermediate insulating layerILD, the nitride layer SIN, may diffuse into the first semiconductorlayer A1 under the gate insulating layer GI. On the contrary, thehydrogen particles going out from the nitride layer SIN may not diffusetoo much into the semiconductor material of the second thin filmtransistor T2 over the gate insulating layer GI. Therefore, the nitridelayer SIN may be deposited as close to the gate insulating layer GI aspossible. In some examples, the nitride layer SIN may selectively coverover the first thin film transistor T1 including the first semiconductorlayer A1, but may not cover where the second thin film transistor T2 isplaced.

Further, considering the manufacturing process, the intermediateinsulating layer ILD, including the nitride layer SIN, may have athickness of 1,000 Å˜3,000 Å. Further, so that much more of the hydrogenparticles from the nitride layer SIN diffuse into the firstsemiconductor layer A1, but without the hydrogen particles affecting thesecond semiconductor layer A2, the oxide layer SIO may be thicker thanthe gate insulating layer GI. In addition, as the oxide layer SIO maycontrol the hydrogen diffusion amount, the oxide layer SIO may bethicker than the nitride layer SIN. In addition, the oxide layer SIO maybe the gate insulating layer for the second thin film transistor T2.Considering these conditions, the oxide layer SIO may have a thicknessof 1,000 Å˜3,000 Å.

A second semiconductor layer A2 overlapping the second gate electrode G2may be disposed on the oxide layer SIO. The second semiconductor layerA2 includes the channel area of the second thin film transistor T2. Forthe case that the second thin film transistor T2 is applied for thedisplay element, it is preferable that the second semiconductor layer A2has characteristics proper to perform the switching element. Forexample, it is preferable that the second semiconductor layer A2includes an oxide semiconductor material, such as indium gallium zincoxide (IGZO), indium gallium oxide (IGO), or indium zinc oxide (IZO).The oxide semiconductor material has a merit for driving the device withrelatively low frequency. Due to these characteristics, the pixels mayhave a long period for holding the pixel voltage, and consequentially,it may be desirable to apply the display with a low frequency driveand/or low power consumption. For the thin film transistor having theoxide semiconductor material, considering the structure in which twodifferent type thin film transistors are formed on the same substrate,it is preferable that the oxide semiconductor thin film transistor has abottom gate structure for ensuring the stability of the elements.

A second source electrode S2 and a second drain electrode D2 may bedisposed on the second semiconductor layer A2 and the oxide layer SIO.The second source electrode S2 and the second drain electrode D2 may bedisposed to face each other with a predetermined distance, and maycontact the upper surfaces of the one side and the other side of thesecond semiconductor layer A2. The second source electrode S2 maycontact the upper surface of the oxide layer SIO and one upper surfaceof the second semiconductor layer A2. The second drain electrode D2 maycontact the upper surface of the oxide layer SIO and the other uppersurface of the second semiconductor layer A2.

On the whole surface of the substrate SUB having the first thin filmtransistor T1 and the second thin film transistor T2, a passivationlayer PAS is deposited. Further, by patterning the passivation layerPAS, contact holes for exposing the first drain electrode D1 and/or thesecond drain electrode D2 may be included. In addition, on thepassivation layer PAS, a pixel electrode (e.g., an anode electrode forthe organic light emitting diode display) may be included as connectingto the first drain electrode D1 and/or second drain electrode D2. Here,for convenience, the structure of the thin film transistor showing themain features of the present disclosure will be explained.

As mentioned above, the thin film transistor substrate for the flatpanel display according to the first embodiment of the presentdisclosure suggests the structure in which the first thin filmtransistor T1 has a polycrystalline semiconductor material and thesecond thin film transistor T2 has an oxide semiconductor material, onthe same one substrate SUB. Especially, the first semiconductor layer A1including the polycrystalline semiconductor material may be disposedunder the first gate electrode G1, and the second semiconductor layer A2including the oxide semiconductor material may be disposed over thesecond gate electrode G2. Further, the second gate electrode G2 may bedisposed over the intermediate insulating layer ILD covering the firstgate electrode G1. The first semiconductor layer A1, which may bemanufactured under a relatively higher temperature condition, may beformed first. After that, the second semiconductor layer A2, which maybe manufactured under a relatively lower temperature condition, may beformed later. As the result, the oxide semiconductor material may not beexposed to the high temperature condition during the whole manufacturingprocesses. As the first semiconductor layer A1 may be formed beforeforming the first gate electrode G1, the first thin film transistor T1may have a top-gate structure. As the second semiconductor layer A1 maybe formed after forming the second gate electrode G2, the second thinfilm transistor T2 may have a bottom-gate structure.

Further, in the thermal treatment process for the second semiconductorlayer A2 including the oxide semiconductor material, the hydrogenationprocess for the first semiconductor layer A1 including thepolycrystalline semiconductor material can be performed, at the sametime. To do so, the intermediate insulating layer ILD may include thenitride layer SIN, and the oxide layer SIO may be stacked on theintermediate insulating layer ILD. In a manufacturing process, ahydrogenation may be used for diffusing the hydrogen particles into thefirst semiconductor layer A1. Further, it may be advantageous to performa thermal treatment for stabilizing the second semiconductor layer A2including the oxide semiconductor material. The hydrogenation processmay be performed after depositing the nitride layer SIN on the firstsemiconductor layer A1, and the thermal treatment may be performed afterforming the second semiconductor layer A2. According to the firstembodiment of the present disclosure, as the oxide layer SIO may bedeposited between the nitride layer SIN and the second semiconductorlayer A2, the hydrogen particles can be prevented from diffusing toomuch into the second semiconductor layer A2 including the oxidesemiconductor material. Therefore, in this first embodiment of thepresent disclosure, during the thermal treatment for the oxidesemiconductor material, the hydrogenation process may be performed atthe same time.

In order for the nitride layer SIN to be close to the firstsemiconductor layer A1 requiring the hydrogenation process, the nitridelayer SIN may be stacked on only the first gate electrode G1. Inaddition, in order for the second semiconductor layer A2 including theoxide semiconductor material to be far away from the nitride layer SIN,the second semiconductor layer A2 may be disposed on the oxide layer SIOcovering the nitride layer SIN and the second gate electrode G2 on thenitride layer SIN. As a result, the hydrogen particles exiting from thenitride layer SIN may be effectively prevented from diffusing too muchinto the second semiconductor layer A2 during the post-thermal process.

The above description using FIG. 1A discussed the basic structures ofthe first and the second thin film transistors. In addition, for anexample in which the second thin film transistor is used for the displayelement disposed in the display area, the gate lines and the data linesmay be further disposed around the pixel area. Further, the gate linesand the data lines may be formed at a same layer with the gate electrodeand the data electrode, respectively. Hereinafter, with regard to FIG.1B, an explanation will be given for how the gate electrode and/or thesource electrode may be connected to the gate line and/or data line.

With reference to FIG. 1B, the structure of the thin film transistor issimilar to that described above for FIG. 1A. Therefore, duplicateexplanation is omitted. When forming the first gate electrode G1 of thefirst thin film transistor T1, with the same material and at the samelayer, a gate line GL may surround the second thin film transistor T2.That is, the gate line GL may be covered by the intermediate insulatinglayer ILD as in the first gate electrode G1.

The intermediate insulating layer ILD may include the source contacthole SH for exposing the source area SA of the first semiconductor layerA1, and the drain contact hole DH for exposing the drain area DA of thefirst semiconductor layer A1. In addition, a gate line contact hole GLHfor exposing some portions of the gate line GL may be further includedat the intermediate insulating layer ILD.

The first source electrode S1, the first drain electrode D1, the secondgate electrode G2, and the data line DL may be disposed on theintermediate insulating layer ILD. The first source electrode S1 maycontact the source area SA through the source contact hole SH. The firstdrain electrode D1 may contact the drain area DA through the draincontact hole DH. The second gate electrode G2 may connect to the gateline GL through the gate line contact hole GHL. The data line DL maycross the gate line GL with the intermediate insulating layer ILD aroundthe second thin film transistor T2.

The first source electrode S1, the first drain electrode D1, and thesecond gate electrode G2 may be covered by the oxide layer SIO. On theoxide layer SIO, a second semiconductor layer A2 may overlap the secondgate electrode G2. The oxide layer SIO may further include a data linecontact hole DLH for exposing some portions of the data line DL.

The second source electrode S2 and the second drain electrode D2 may bedisposed on the second semiconductor layer A2 and the oxide layer SIO.The second source electrode S2 may contact one upper side of the secondsemiconductor layer A2, and may connect to the data line DL through thedata line contact hole DLH. The second drain electrode D2 may contactanother upper side of the second semiconductor layer A2.

FIG. 2 is a flow chart illustrating a method for manufacturing a thinfilm transistor substrate having two different types of thin filmtransistors according to the first embodiment of the present disclosure.

In operation S100, on a substrate SUB, a buffer layer BUF is deposited.Even though it is not shown in figures, before depositing the bufferlayer BUF, a light shield layer may be formed at a desired area.

In operation S110, on the buffer layer BUF, an amorphous silicon (a-Si)material is deposited. Performing the crystallization process, theamorphous silicon layer is converted into the polycrystalline silicon(poly-Si). Using a first mask process, the polycrystalline silicon layeris patterned to form a first semiconductor layer A1.

In operation S120, by depositing an insulating material, such as siliconoxide, on the whole surface of the substrate SUB having the firstsemiconductor layer A1, a gate insulating layer GI is formed. The gateinsulating layer GI preferably includes the silicon oxide. Here, thegate insulating layer GI may have a thickness of 1,000 Å˜1,500 Å.

In operation S200, on the gate insulating layer GI, a gate metalmaterial may be deposited. Using a second mask process, the gate metallayer may be patterned to form a first gate electrode G1. The first gateelectrode G1 may overlap the middle portion of the first semiconductorlayer A1.

In operation S210, using the first gate electrode G1 as a mask, impuritymaterials are doped into some portions of the first semiconductor layerA1 so that doping areas including a source area SA and a drain area DAmay be defined. The detailed manufacturing process for the doping areasmay be little bit different according to the types of thin filmtransistor (e.g., P MOS type, N-MOS type and/or C-MOS type). For examplefor the N-MOS type, a high density doping area may be formed first, andthen a low density doping area may be formed. Using the photo-resistpattern for the first gate electrode G1 which has a wider size than thefirst gate electrode G1, the high density doping area can be defined.Removing the photo-resist pattern and using the first gate electrode G1as a mask, the low density doping (LDD) area can be defined between thehigh density doping area and the first gate electrode G1. The impuritydoping areas are not shown in the figures, for convenience.

In operation S220, on the whole surface of the substrate SUB having thefirst gate electrode G1, an intermediate insulating layer ILD may bedeposited using a nitride inorganic material, such as a silicon nitride(SiN_(x)) material. The nitride layer SIN may include many hydrogenparticles during the depositing process. In consideration of themanufacturing process and the hydrogenation efficiency, the nitridelayer SIN of the intermediate insulating layer ILD may have a thicknessof 1,000 Å˜3,000 Å.

In operation 300, using a third mask process, the intermediateinsulating layer ILD may be patterned to form a source contact hole SHexposing one portion of the first semiconductor layer A1, and a draincontact hole DH exposing another portion of the first semiconductorlayer A1. These contact holes are for connecting the source-drainelectrodes to the first semiconductor layer A1.

In operation S400, a metal material may be deposited on the intermediateinsulating layer ILD. Using the fourth mask process, the metal materialmay be patterned for a first source electrode S1, a first drainelectrode D1, and a second gate electrode G2. The first source electrodeS1 may connect to the one portion of the first semiconductor layer A1through the source contact hole SH. The first drain electrode D1 mayconnect to the other portion of the first semiconductor layer A1 throughthe drain contact hole DH. The second gate electrode G2 may be disposedwhere the second thin film transistor T2 is placed.

In operation S410, an oxide layer SIO may be deposited using the oxideinorganic material, such as a silicon oxide (SiO_(x)) material, on thewhole surface of the substrate SUB having the first source electrode S1,the first drain electrode D1, and the second gate electrode G2. In thesecond thin film transistor T2, the oxide layer SIO may also act as agate insulating layer as covering the second gate electrode G2. Theoxide layer SIO may have thickness of 1,000 Å˜3,000 Å. The thicknessesof the oxide layer SIO and the intermediate insulating layer ILD(including the nitride layer SIN) may be selected and/or decided inconsideration of the hydrogen diffusion efficiency and the elementproperties. For example, to prevent the hydrogen particles fromdiffusing out too much, the nitride layer SIN may be thinner than theoxide layer SIO.

In operation S500, an oxide semiconductor material may be deposited onthe oxide layer SIO. The oxide semiconductor material includes at leastone of Indium Gallium Zinc Oxide (IGZO), Indium Gallium Oxide (IGO), andIndium Zinc Oxide (IZO). Using a fifth mask process, the oxidesemiconductor material may be patterned to form a second semiconductorlayer A2. The second semiconductor layer A2 may overlap the second gateelectrode G2.

In operation S510, performing a post-thermal process to the substrateSUB having the second semiconductor layer A2, the hydrogenation for thefirst semiconductor layer A1 including the polycrystalline silicon, andthe thermal treatment for the second semiconductor layer A2 includingthe oxide semiconductor material may be performed at the same time. Thepost-thermal process may be performed under 350˜380° C. temperatureconditions. At this time, a large amount of the hydrogen particlesincluded into the nitride layer SIN may be diffused into the firstsemiconductor layer A1. However, the amount of the hydrogen particlesdiffused into the second semiconductor layer A2 may be restricted and/orcontrolled by the oxide layer SIO. In some embodiments, thehydrogenation process for the first semiconductor layer A1 may performedseparately from the thermal treatment for the second semiconductor layerA2. In such examples, the hydrogenation process may be firstly performedafter operation S220 for depositing the intermediate insulating layerILD, and then the thermal treatment for the second semiconductor layerA2 may be performed by this post-thermal process.

In operation S600, a source-drain metal material may be deposited on thewhole surface of the substrate SUB having the second semiconductor layerA2. Using a sixth mask process, the source-drain metal material may bepatterned to form a second source electrode S2 and a second drainelectrode D2. The second source electrode S2 may contact the uppersurface of the one side of the second semiconductor layer A2 and theupper surface of the second intermediate insulating layer ILD2. Thesecond drain electrode D2 may contact the upper surface of the otherside of the second semiconductor layer A2 and the upper surface of theoxide layer SIO.

In operation S700, a passivation layer PAS may be deposited on the wholesurface of the substrate SUB having the first thin film transistor T1and the second thin film transistor T2. Even though not shown in thefigures, the passivation layer PAS may be patterned to form contactholes for exposing some portions of the first and/or second drainelectrodes D1 and/or D2.

Second Embodiment

FIG. 3 is a cross sectional view illustrating a structure of a thin filmtransistor substrate for a flat panel display in which two differenttypes of thin film transistors are formed according to a secondembodiment of the present disclosure.

The thin film transistor substrate according to the second embodiment issimilar to that of the first embodiment. One difference is that, in theFIG. 3 example, the intermediate layer ILD has a double-layer structure.The intermediate insulating layer ILD may include a nitride layer SINand a lower oxide layer SIO2. For example, the lower oxide layer SIO2may be stacked on a nitride layer SIN. Otherwise, the nitride layer SINmay be stacked on the lower oxide layer SIO2. Here, the “lower” of thelower oxide layer SIO2 is so named because it is disposed under theoxide layer SIO, but the term “lower” does not mean that the lower oxidelayer SIO2 is disposed under the nitride layer SIN.

By the post-thermal process, the hydrogen particles in the nitride layerSIN may be diffused into the first semiconductor layer A1. Inconsideration of the diffusion efficiency, the nitride layer SIN of theintermediate insulating layer ILD may have a thickness of 1,000 Å˜3,000Å. As the lower oxide layer SIO2 may compensate for a damaged surfacecondition of the gate insulating layer GI during the patterning processfor the gate electrode G1 (under the nitride layer SIN), or may ensurethe stability of the nitride layer SIN (over the nitride layer SIN), thelower oxide layer SIO2 may have a thickness of 500 Å˜1,000 Å.

An oxide layer SIO may be deposited on the intermediate insulating layerILD including the lower oxide layer SIO2 and the nitride layer SIN. Theoxide layer SIO may also act as a gate insulating layer for the secondthin film transistor T2. If the oxide layer SIO is too thick, the gatevoltage may not be properly applied to the second semiconductor layerA2. Therefore, the thickness of the oxide layer SIO may have a thicknessof 1,000 Å˜3,000 Å. In addition, the gate insulating layer GI may have athickness of 1,000˜1,500 Å.

In the above description using FIG. 3, the intermediate insulating layerILD has a double-layered structure in which the nitride layer SIN isstacked on the lower oxide layer SIO2. In some examples, theintermediate insulating layer ILD may have a double-layered structure inwhich the nitride layer SIN is stacked under the lower oxide layer SIO2.In such case, the nitride layer SIN may be closer to the firstsemiconductor layer A1, and may be further from the second semiconductorlayer A2 due to the thickness of the lower oxide layer SIO2. Therefore,the hydrogen particles may be more easily diffused into the firstsemiconductor layer A1, but they may be prevented from diffusing intothe second semiconductor layer A2.

In one example, in consideration of the manufacturing process, theintermediate insulating layer ILD may have a thickness of 2,000 Å˜6,000Å. The thickness of each of the nitride layer SIN and the lower oxidelayer SIO2 may be 1,000 Å˜3,000 Å, respectively. Further, consideringthat the oxide layer SIO is the gate insulating layer for the secondthin film transistor T2, the oxide layer SIO may have a thickness of1,000 Å˜3,000 Å.

As other elements are similar with those of the first embodiment, adetailed explanation is omitted. Hereinafter, the method formanufacturing the thin film transistor substrate for flat panel displayaccording to the second embodiment of the present disclosure will beexplained. Here, the duplicated explanations having no extra meaning arenot mentioned.

FIG. 4 is a flow chart illustrating a method for manufacturing a thinfilm transistor substrate for a flat panel display in which twodifferent types of thin film transistors are formed according to thesecond embodiment of the present disclosure.

In operation S100, on a substrate SUB, a buffer layer BUF is deposited.In operation S110, on the buffer layer BUF, an amorphous silicon (a-Si)material is deposited. Performing the crystallization process, theamorphous silicon layer is converted into the polycrystalline silicon(poly-Si). Using a first mask process, the polycrystalline silicon layeris patterned to form a first semiconductor layer A1.

In operation S120, by depositing an insulating material, such as siliconoxide, on the whole surface of the substrate SUB having the firstsemiconductor layer A1, a gate insulating layer GI is formed. The gateinsulating layer GI is preferably made of silicon oxide with a thicknessof 1,000 Å˜1,500 Å.

In operation S200, on the gate insulating layer GI, a gate metalmaterial is deposited. Using a second mask process, the gate metal layeris patterned to form a first gate electrode G1. The first gate electrodeG1 may overlap the middle portion of the first semiconductor layer A1.

In operation S210, using the first gate electrode G1 as a mask, impuritymaterials are doped into some portions of the first semiconductor layerA1 so that doping areas including a source area SA and a drain area DAmay be defined.

In operation S220, an intermediate insulating layer ILD may be depositedon the whole surface of the substrate SUB having the first gateelectrode G1. For example, the intermediate layer ILD may have thedouble-layered structure having a lower oxide layer SIO2 and a nitridelayer SIN. In one example, the lower oxide layer SIO2 may be stacked onthe nitride layer SIN. In another example, the nitride layer SIN may bestacked on the lower oxide layer SIO2. In an example in which the loweroxide layer SIO2 is stacked at the lower layer, the lower oxide layerSIO2 may have a thickness of 500 Å˜1,000 Å. The nitride layer SIN mayhave a thickness of 1,000 Å˜3,000 Å. In an example in which the nitridelayer SIN is stacked at the lower layer, the lower oxide layer SIO2 andthe nitride layer SIN may have a thickness of 1,000 Å˜3,000 Å forpreventing the hydrogen particles from diffusing too much into thesecond semiconductor layer A2.

In operation S300, using a third mask process, the intermediateinsulating layer ILD may be patterned to form a source contact hole SHexposing one portion of the first semiconductor layer A1, and a draincontact hole DH exposing another portion of the first semiconductorlayer A1.

In operation S400, on the intermediate insulating layer ILD, a metalmaterial may be deposited. Using a fourth mask process, the metalmaterial may be patterned to form a first source electrode S1, a firstdrain electrode D1, and a second gate electrode G2. The first sourceelectrode S1 may connect to the one portion of the first semiconductorlayer A1 through the source contact hole SH. The first drain electrodeD1 may connect to the other portion of the first semiconductor layer A1through the drain contact hole DH. The second gate electrode G2 may bedisposed where the second thin film transistor T2 is placed.

In operation S410, an oxide layer SIO may be deposited using an oxideinorganic material, such as a silicon oxide (SiO_(x)) material, on thewhole surface of the substrate SUB having the first source electrode S1,the first drain electrode D1, and the second gate electrode G2. Theoxide layer SIO may also act as a gate insulating layer for the secondthin film transistor T2. Therefore, the oxide layer SIO may have athickness of 1,000 Å˜3,000 Å.

In operation S500, an oxide semiconductor material may be deposited onthe oxide layer SIO. Using a fifth mask process, the oxide semiconductormaterial may be patterned to form a second semiconductor layer A2. Thesecond semiconductor layer A2 may overlap the second gate electrode G2.

In operation S510, performing a post-thermal process to the substrateSUB having the second semiconductor layer A2, the hydrogenation for thefirst semiconductor layer A1 including the polycrystalline silicon, andthe thermal treatment for the second semiconductor layer A2 includingthe oxide semiconductor material may be performed at the same time. Thepost-thermal process may be performed under 350˜380° C. temperatureconditions. At this time, a large amount of the hydrogen particlesincluded into the nitride layer SIN may be diffused into the firstsemiconductor layer A1. However, the amount of the hydrogen particlesdiffused into the second semiconductor layer A2 may be restricted and/orcontrolled by the oxide layer SIO. In some examples, the hydrogenationprocess for the first semiconductor layer A1 may be performed separatelyfrom the thermal treatment for the second semiconductor layer A2.

In operation S600, a source-drain metal material may be deposited on thewhole surface of the substrate SUB having the second semiconductor layerA2. Using a sixth mask process, the source-drain metal material may bepatterned to form a second source electrode S2 and a second drainelectrode D2.

In operation S700, a passivation layer PAS may be deposited on the wholesurface of the substrate SUB having the first and the second thin filmtransistors T1 and T2.

Third Embodiment

FIG. 5 is a cross sectional view illustrating a structure of a thin filmtransistor substrate for a flat panel display in which two differenttype thin film transistors are formed according to the third embodimentof the present disclosure.

The thin film transistor substrate according to the third embodiment issimilar to that of the first and the second embodiments. One differenceis that the oxide may act as the intermediate insulating layer for thefirst thin film transistor T1, and as the gate insulating layer for thesecond thin film transistor T2. For example, the intermediate layer ILDmay include a first intermediate insulating layer ILD1 and a secondintermediate insulating layer ILD2. The first intermediate insulatinglayer ILD1 may have a double-layer structure in which a lower oxidelayer SIO2 and a nitride layer SIN are stacked. Further, the nitridelayer SIN may be selectively disposed over only the first area where thefirst thin film transistor T1 is located, but not in the second areawhere the second thin film transistor T2 is located. The secondintermediate insulating layer ILD2 may include the oxide layer SIOcovering the nitride layer SIN as the gate insulating layer for thesecond thin film transistor T2.

Where the first thin film transistor T1 is placed, by the post-thermalprocess, the hydrogen particles in the nitride layer SIN may be diffusedinto the first semiconductor layer A1. Considering the hydrogenationefficiency, the nitride layer SIN may have a thickness of 1,000 Å˜3,000Å. Further, the lower oxide layer SIO may have a thickness of 500Å˜1,000 Å.

Even when the nitride layer SIN may have a 3,000 Å thickness, it may bedisposed apart from the second thin film transistor T2. Therefore, thepossibility of the hydrogen diffusion into the second semiconductorlayer A2 is low. Further, as the oxide layer SIO of the secondintermediate insulating layer ILD2 may be stacked on the nitride layerSIN, the hydrogen diffusion into the second semiconductor layer A2 maybe more effectively prevented.

In the third embodiment, unlike the first and the second embodiments,the first source-drain electrodes S1 and D1 may be made of the samematerial and at a same layer with the second source-drain electrodes S2and D2.

As other elements are similar with those of the first and secondembodiments, a detailed explanation is omitted. Hereinafter, the methodfor manufacturing the thin film transistor substrate for flat paneldisplay according to the third embodiment of the present disclosure willbe explained. Here, the duplicated explanations having no extra meaningare not mentioned.

FIG. 6 is a flow chart illustrating a method for manufacturing the thinfilm transistor substrate for a flat panel display in which twodifferent type thin film transistors are formed, according to the thirdembodiment of the present disclosure.

In operation S100, on a substrate SUB, a buffer layer BUF is deposited.

In operation S110, on the buffer layer BUF, an amorphous silicon (a-Si)material is deposited. Performing the crystallization process, theamorphous silicon layer is converted into the polycrystalline silicon(poly-Si). Using a first mask process, the polycrystalline silicon layeris patterned to form a first semiconductor layer A1.

In operation S120, by depositing an insulating material, such as siliconoxide, on the whole surface of the substrate SUB having the firstsemiconductor layer A1, a gate insulating layer GI is formed. The gateinsulating layer GI preferably includes the silicon oxide. Here, thegate insulating layer GI may have a thickness of 1,000 Å˜1,500 Å.

In operation S200, on the gate insulating layer GI, a gate metalmaterial is deposited. Using a second mask process, the gate metal layeris patterned to form a first gate electrode G1 for the first thin filmtransistor T1. The first gate electrode G1 is disposed as overlappingwith the middle portion of the first semiconductor layer A1.

In operation S210, using the first gate electrode G1 as a mask, impuritymaterials are doped into some portions of the first semiconductor layerA1 so that doping areas including a source area SA and a drain area DAmay be defined.

In operation S220, a first intermediate insulating layer ILD1 may bedeposited on the whole surface of the substrate SUB having the firstgate electrode G1. For example, the first intermediate layer ILD1 mayhave the double-layered structure having a lower oxide layer SIO2 and anitride layer SIN. In one example, the lower oxide layer SIO2 may bestacked on the nitride layer SIN. In another example, the nitride layerSIN may be stacked on the lower oxide layer SIO2. For an example inwhich the lower oxide layer SIO2 is stacked under the nitride layer SIN,the lower oxide layer SIO2 may have a thickness of 500 Å˜1,000 Å. Thenitride layer SIN may have a thickness of 1,000 Å˜3,000 Å. For anexample in which the nitride layer SIN is stacked under the lower oxidelayer SIO2, the lower oxide layer SIO2 may have a thickness of 1,000Å˜3,000 Å, similar to the nitride layer SIN, for preventing the hydrogenparticles diffusing too much into the second semiconductor layer A2.

In operation S300, using a third mask process, the nitride layer SIN ofthe first intermediate insulating layer ILD1 may be patterned to coveronly the first semiconductor layer A1. In an example in which thenitride layer SIN is stacked at the lower layer, the lower oxide layerSIO2 may be deposited after depositing and patterning the nitride layerSIN. In an example in which the nitride layer SIN is stacked at theupper layer, the lower oxide layer SIO2 and the nitride layer SIN may besequentially deposited, and then only the nitride layer SIN may bepatterned.

In operation S400, a gate metal material may be deposited on the firstintermediate insulating layer ILD1 including the nitride layer SINselectively covering the first semiconductor layer A1. Using a fourthmask process, the gate metal material may be patterned to form a secondgate electrode G2. The second gate electrode G2 may be disposed wherethe second thin film transistor T2 is placed.

In operation S410, on the whole surface of the substrate SUB having thesecond gate electrode G2, a second intermediate insulating layer ILD2may be deposited using an oxide inorganic material, such as a siliconoxide (SiO_(x)) material.

In operation S500, an oxide semiconductor material may be deposited onthe second intermediate insulating layer ILD2. Using a fifth maskprocess, the oxide semiconductor material may be patterned to form asecond semiconductor layer A2. The second semiconductor layer A2 mayoverlap the second gate electrode G2.

In operation S510, performing a post-thermal process to the substrateSUB having the second semiconductor layer A2, the hydrogenation for thefirst semiconductor layer A1 including the polycrystalline silicon, andthe thermal treatment for the second semiconductor layer A2 includingthe oxide semiconductor material may be performed at the same time. Thepost-thermal process may be performed under 350˜380° C. temperaturecondition. In some examples, the hydrogenation process for the firstsemiconductor layer A1 may be performed separately from the thermaltreatment for the second semiconductor layer A2. In such examples, alarge amount of the hydrogen particles included into the nitride layerSIN may be diffused into the first semiconductor layer A1. However,because the nitride layer SIN may cover only the first area where thefirst channel layer A1 is located, the amount of the hydrogen particlesinto the second channel layer A2 may be restricted and/or controlled.

In operation S600, after performing the post-thermal treatment to thesemiconductor layers, using a sixth mask process, the secondintermediate insulating layer ILD2 and the first intermediate insulatinglayer ILD1 may be patterned to form the source contact hole SH and thedrain contact hole DH.

In operation S700, a source-drain metal material may be deposited on thewhole surface of the substrate SUB having the contact holes SH and DHand the second semiconductor layer A2. Using a seventh mask process, thesource-drain metal material may be patterned to form a first sourceelectrode S1, a first drain electrode D1, a second source electrode S2,and a second drain electrode D2.

In operation S800, a passivation layer PAS may be deposited on the wholesurface of the substrate SUB having the first and the second thin filmtransistors T1 and T2.

First Application Example

The thin film transistor substrate having two different type thin filmtransistors on the same substrate, above explained, can be applied tovarious type display including the flat panel display, the flexibledisplay and/or the curved display. By forming the different two types ofthin film transistors on the same substrate, various advantages can beachieved. FIG. 7 is a block diagram illustrating a structure of thedisplay according to a first application example of the presentdisclosure. With reference to FIG. 7, advanced features and meritsexpected from the thin film transistor substrate according to a firstapplication example of the present disclosure will be explained.

The first and the second transistors T1 and T2 would be formed in eachpixel of the display panel 100 for switching the data voltage applied tothe pixel or for driving the pixel. In the case of an organic lightemitting diode display, the second thin film transistor T2 may be aswitch element for the pixel, and the first thin film transistor T1 maybe a driver element. In the interim, by combining the first and thesecond thin film transistors T1 and T2, they may be applied to oneswitch element or one driver element.

For a mobile device or a wearable device, in order to reduce the powerconsumption, the lower speed driving method using a low frame rate isadopted. In this case, the frame frequency may be lowered for stillimage and/or images having a slower update interval. Here, when usingthe lower frame rate, at every time for changing the data voltage, thebrightness of the display may be flashed. In some cases, as thedischarging time interval is elongated, the brightness may be flickeredat every data update period. By applying the first and the second thinfilm transistors T1 and T2 according to the present disclosure, theflicker problem at lower speed driving method can be prevented.

In the lower speed driving method, as the data update period iselongated, the leaked current amount of the switching thin filmtransistor may be increased. The leaked current of the switching thinfilm transistor may cause a voltage drop down of the storage capacitanceand a drop down of the voltage between gate and source. The second thinfilm transistor having the oxide semiconductor material can be appliedto the switch thin film transistor of the organic light emitting diodedisplay. Because the thin film transistor including the oxidesemiconductor material has lower off-current characteristics, thevoltage drop down of the storage capacitance and/or of the gateelectrode of the driving thin film transistor is prevented. The flickerphenomenon does not occur when using the lower speed driving method.

As polycrystalline silicon has the characteristics of high mobility, byapplying the first thin film transistor to the driving thin filmtransistor of the organic light emitting diode display, the currentamount supplied to the organic light emitting diode can be enlarged.Therefore, by applying the second thin film transistor T2 to theswitching thin film transistor and the first thin film transistor T1 tothe driving thin film transistor, the organic light emitting diodedisplay can achieve lower power consumption and better video quality.

As the thin film transistor substrate according to the presentdisclosure has excellent video quality without flickers even though thelower speed driving method is applied, it has a merit of being verysuitable for applying to the mobile display or the wearable display. Forthe example of wearable wrist watch, the video data may be updated atevery one second for reducing the power consumption. In that case, theframe frequency may be 1 Hz. Using the arrangement of the presentdisclosure, excellent video quality without flickering can be achievedeven though the video data is driven with lower frequency, such as 1 Hzor less. Further, for the mobile display or the wearable display, theframe rate for the still image can be remarkably lowered, so that thepower consumption can be saved without any degradation of the videoquality. As the result, the video quality of the mobile display and/orwearable display, and the life time of the battery can be elongated. Inaddition, the present disclosure can be applied to the electric bookdevice (or “E-Book”) of which the data update period is very long,without any degradation of the video quality.

At least one of the first and the second thin film transistors T1 and T2may be embedded into a driver IC, for example shown in FIG. 7, e.g., anyone of the data driver IC 200, the multiplexer (MUX) 210, and the gatedriver IC 300, for forming the driver IC. This driver IC writes and/orapplies the data voltage to the pixel. In another case, any one of thefirst and the second thin film transistors T1 and T2 is disposed withinthe pixel, and the other is disposed in the driver IC. The data driverIC 200 converts the input video data into the voltage values and outputthe voltage values. The multiplexer 210 may reduce the number of theoutput channel of the data driver 200, by distributing the data voltagesfrom the data driver 200 to the data lines DL by time-sharing ortime-division method. The gate driver IC 300 outputs the scan signal (or“gate signal”) to the gate line GL synchronized to the data voltage forsequentially selecting the pixel line where the data voltage is applied.In order to reduce the output channel number of the gate driver IC 300,other multiplexers not shown in the figures may be further includedbetween the gate driver IC 300 and the gate line GL. The multiplexer 210and the gate driver IC 300 may be formed on the same thin filmtransistor substrate within the pixel array, as shown in FIG. 7. Themultiplexer 210 and the gate driver IC 300 may be disposed within thenon-display area NA and the pixel array may be disposed within thedisplay area AA, as shown in FIG. 7.

The thin film transistor substrate according to the present disclosuremay be applied to any type of active type display using an active matrixthin film transistor substrate, such as the liquid crystal display, theorganic light emitting diode display, and/or the electrophoresis displaydevice. Hereinafter, more application examples for the display using thethin film transistor substrate according to the present disclosure willbe explained.

Second Application Example

FIG. 8 is a plane view illustrating a thin film transistor substratehaving an oxide semiconductor layer included in a fringe field typeliquid crystal display according to a second application example of thepresent disclosure. FIG. 9 is a cross-sectional view illustrating thestructure of the thin film transistor substrate of FIG. 8 by cuttingalong the line I-I′ according to the second application example of thepresent disclosure.

The thin film transistor substrate having a metal oxide semiconductorlayer shown in FIGS. 8 and 9 comprises a gate line GL and a data line DLcrossing each other with a gate insulating layer GI therebetween on alower substrate SUB, and a thin film transistor T formed at eachcrossing portion. By the crossing structure of the gate line GL and thedata line DL, a pixel area is defined.

The thin film transistor T comprises a gate electrode G branched (or“extruded”) from the gate line GL, a source electrode S branched fromthe data line DL, a drain electrode D facing the source electrode S, anda semiconductor layer A overlapping with the gate electrode G on thegate insulating layer GI for forming a channel area between the sourceelectrode S and the drain electrode D.

At one end of the gate line GL, a gate pad GP is disposed for receivingthe gate signal. The gate pad GP is connected to a gate pad intermediateterminal IGT through the first gate pad contact hole GH1 penetrating thegate insulating layer GI. The gate pad intermediate terminal IGT isconnected to the gate pad terminal GPT through the second gate padcontact hole GH2 penetrating the first passivation layer PA1 and thesecond passivation layer PA2. Further, at one end of the data line DL, adata pad DP is disposed for receiving the pixel signal. The data pad DPis connected to a data pad terminal DPT through the data pad contacthole DPH penetrating the first passivation layer PA1 and the secondpassivation layer PA2.

In the pixel area, a pixel electrode PXL and a common electrode COM areformed with the second passivation layer PA2 there-between, to form afringe electric field. The common electrode COM is connected to thecommon line CL disposed in parallel with the gate line GL. The commonelectrode COM is supplied with a reference voltage (or “common voltage”)via the common line CL. For other cases, the common electrode COM hasthe one sheet electrode shape which covers the whole surface of thesubstrate SUB except the drain contact hole DH portions. That is,covering over the data line DL, the common electrode COM can work as ashielding means for the data line DL.

The common electrode COM and the pixel electrode PXL can have variousshapes and positions according to the design purpose and environment.While the common electrode COM is supplied with a reference voltagehaving constant value, the pixel electrode PXL is supplied with a datavoltage varying timely according to the video data. Therefore, betweenthe data line DL and the pixel electrode PXL, a parasitic capacitancemay be formed. Due to the parasitic capacitance, the video quality ofthe display may be degraded. Therefore, it is preferable that the commonelectrode COM is disposed at the lower layer and the pixel electrode PXLis disposed at the topmost layer.

In other words, on the first passivation layer PA1 covering the dataline DL and the thin film transistor T, a planarization layer PAC isstacked thereon by thickly depositing an organic material having a lowpermittivity. Then, the common electrode COM is formed. And then, afterdepositing the second passivation layer PA2 to cover the commonelectrode COM, the pixel electrode PXL overlapping with the commonelectrode is formed on the second passivation layer PA2. In thisstructure, the pixel electrode PXL is far from the data line DL by thefirst passivation layer PA1, the planarization layer PAC and the secondpassivation layer PA2, so that it is possible to reduce the parasiticcapacitance between the data line DL and the pixel electrode PXL. Inother case, the pixel electrode PXL may be disposed at the lower layerand the common electrode COM is disposed at the topmost layer.

The common electrode COM may have a rectangular shape corresponding tothe pixel area. The pixel electrode PXL may have the shape of aplurality of segments. Especially, the pixel electrode PXL is verticallyoverlapped with the common electrode COM with the second passivationlayer PA2 there-between. Between the pixel electrode PXL and the commonelectrode COM, the fringe electric field is formed. By this fringeelectric field, the liquid crystal molecules arrayed in plane directionbetween the thin film transistor substrate and the color filtersubstrate may be rotated according to the dielectric anisotropy of theliquid crystal molecules. According to the rotation degree of the liquidcrystal molecules, the light transmittance ratio of the pixel area maybe changed to represent desired gray scale.

In FIGS. 8 and 9 for explaining the second application example of thepresent disclosure, in convenience, the thin film transistor T of theliquid crystal display is shown briefly. The first and/or the secondthin film transistors T1 and/or T2 explained from the first to secondembodiments of the present disclosure can be applied to this thin filmtransistor. In one example, for a low speed driving, the second thinfilm transistor T2 having the oxide semiconductor material can beapplied to the thin film transistor T. In another example, for low powerconsumption, the first thin film transistor T1 having thepolycrystalline semiconductor material may be applied to the thin filmtransistor T. In still another example, the thin film transistor T maybe formed as including the first and the second thin film transistors T1and T2 and they are connected so that their performance andcharacteristics can compensate each other.

Third Application Example

FIG. 10 is a plane view illustrating the structure of one pixel for theactive matrix type organic light emitting diode display having theactive switching elements such as the thin film transistors according toa third application example of the present disclosure. FIG. 11 is across sectional view illustrating the structure of the organic lightemitting diode display along to the cutting line of II-II′ in FIG. 10according to the third application example of the present disclosure.

With reference to FIGS. 10 and 11, the active matrix type organic lightemitting diode display comprises a switching thin film transistor ST, adriving thin film transistor DT connected to the switching thin filmtransistor ST, and an organic light emitting diode OLE connected to thedriving thin film transistor DT.

The switching thin film transistor ST is formed where a gate line GL anda data line DL are crossing each other, on a substrate SUB. Supplyingthe data voltage from the data line DL to the gate electrode DG of thedriving thin film transistor DT and to the storage capacitance STGreplying the scan signal, the switching thin film transistor ST acts forselecting the pixel which is connected to the switching thin filmtransistor ST. The switching thin film transistor ST includes a gateelectrode SG branching from the gate line GL, a semiconductor channellayer SA overlapping with the gate electrode SG, a source electrode SSand a drain electrode SD. Controlling the amount of the current appliedto the organic light emitting diode OLE of the pixel according to thegate voltage, the driving thin film transistor DT acts for driving theorganic light emitting diode OLE disposed at the pixel selected by theswitching thin film transistor ST.

The driving thin film transistor DT includes a gate electrode DGconnected to the drain electrode SD of the switching thin filmtransistor ST, a semiconductor channel layer DA, a source electrode DSconnected to the driving current line VDD, and a drain electrode DD. Thedrain electrode DD of the driving thin film transistor DT is connectedto the anode electrode ANO of the organic light emitting diode OLE.Between the anode electrode ANO and the cathode electrode CAT, anorganic light emitting layer OL is disposed. The cathode electrode CATis connected to the ground line VSS.

With more detailed reference to FIG. 11, on the substrate SUB of theactive matrix organic light emitting diode display, the gate electrodesSG and DG of the switching thin film transistor ST and the driving thinfilm transistor DT, respectively are disposed. On the gate electrodes SGand DG, the gate insulator GI is deposited. On the gate insulator GIoverlapping with the gate electrodes SG and DG, the semiconductor layersSA and DA are disposed, respectively. On the semiconductor layer SA andDA, the source electrodes SS and DS and the drain electrodes SD and DDfacing and separated from each other, respectively, are disposed. Thedrain electrode SD of the switching thin film transistor ST is connectedto the gate electrode DG of the driving thin film transistor DT via thedrain contact hole DH penetrating the gate insulator GI. The passivationlayer PAS is deposited on the substrate SUB having the switching thinfilm transistor ST and the driving thin film transistor DT.

A color filer CF is disposed at the area where the anode electrode ANOis disposed. It is preferable for the color filter CF to have a largearea as possible. For example, it is preferable to overlap with someportions of the data line DL, the driving current line VDD and/or thegate line GL. The upper surface of the substrate having these thin filmtransistors ST and DT and color filters CF is not in an even and/orsmooth condition, but in an uneven and/or rugged condition having manysteps. In order that the organic light emitting diode display has goodluminescent quality over the whole display area, the organic lightemitting layer OL should have an even or smooth surface. So, to make theupper surface in a planar and even condition, the planar layer PAC orthe overcoat layer OC is deposited on the whole surface of the substrateSUB.

Then, on the overcoat layer OC, the anode electrode ANO of the organiclight emitting diode OLED is disposed. Here, the anode electrode ANO isconnected to the drain electrode DD of the driving thin film transistorDT through the pixel contact hole PH penetrating the overcoat layer OCand the passivation layer PAS.

On the substrate SUB having the anode electrode ANO, a bank (or “bankpattern”) BA is disposed over the area having the switching thin filmtransistor ST, the driving thin film transistor DT and the various linesDL, GL and VDD, for defining the pixel area. The exposed portion of theanode electrode ANO by the bank BA is the light emitting area. On theanode electrode ANO exposed from the bank BA, the organic light emittinglayer OL is deposited. On the organic light emitting layer OL, thecathode electrode ACT is deposited. For the case that the organic lightemitting layer OL has a material emitting the white light, each pixelcan represent various colors by the color filter CF disposed under theanode electrode ANO. The organic light emitting diode display as shownin FIG. 11 is the bottom emission type display in which the visiblelight is radiated to the bottom direction of the display substrate.

Between the gate electrode DG of the driving thin film transistor DT andthe anode electrode ANO, a storage capacitance STG may be formed. Byconnected to the driving thin film transistor DT, the storagecapacitance STG keeps the voltage supplied to the gate electrode DG ofthe driving thin film transistor DT from the switching thin filmtransistor ST in stable condition.

Using the thin film transistor substrate like the above explanations, anactive type flat panel display having good properties can be acquired.Especially, to ensure excellent driving properties, it is preferablethat the active layer of the thin film transistor would include a metaloxide semiconductor material.

The metal oxide semiconductor material may be degraded when it isworking exposed by the light for a long time. Therefore, it ispreferable that the thin film transistor having a metal oxidesemiconductor material has a structure for blocking light from outsideof the upper portion and/or the lower portion of the thin filmtransistor. For example, for the above mentioned thin film transistorsubstrates, it is preferable that the thin film transistor would beformed in the bottom gate structure. That is, the light induced from theoutside of the substrate, especially from the lower side of thesubstrate facing the observer, can be blocked by the gate electrode Gincluding an opaque metal material.

The thin film transistor substrate for the flat panel display has aplurality of pixel area disposed in a matrix manner. Further, each pixelarea includes at least one thin film transistor. That is, over the wholesubstrate, a plurality of thin film transistor is disposed. Theplurality of pixel area and the plurality of thin film transistor areused for the same purpose and they should have the same quality andcharacteristics, so that they have the same structure.

However, in some cases, the thin film transistors may be formed ashaving different characteristics from each other. For the example of theorganic light emitting diode display, in one pixel area, at least oneswitching thin film transistor ST and at least one driving thin filmtransistor DT are disposed. As the purposes of the switching thin filmtransistor ST and the driving thin film transistor DT are different fromeach other, the characteristics of the two are different from each otheras well. To do so, the switch thin film transistor ST and the drivingthin film transistor DT may have the same structure and the samesemiconductor material, but the channel layers of them have differentsizes for optimizing their characteristics. Otherwise, a compensatingthin film transistor may further be included for supporting any specificfunctions or properties of any thin film transistor.

In FIGS. 10 and 11, the switching thin film transistor ST and thedriving thin film transistor DT of the organic light emitting diodedisplay of the third application example are shown. The first and/or thesecond thin film transistors T1 and/or T2 explained from the first tosecond embodiments of the present disclosure can be applied to this thinfilm transistor. For example, the second thin film transistor T2 havingthe oxide semiconductor material can be applied for the switching thinfilm transistor ST. The first thin film transistor T1 having thepolycrystalline semiconductor material may be applied for the drivingthin film transistor DT. Therefore, by including the first and thesecond thin film transistors T1 and T2 on one substrate, theirperformance and characteristics can compensate each other.

Fourth Application Example

For still another example, a driver element (or “driver IC”) may beformed in the non-display area of the same thin film transistorsubstrate for the flat panel display. Hereinafter, with reference toFIGS. 12 and 13, a thin film transistor substrate having the driver ICon the same substrate will be explained.

FIG. 12 is an enlarged plane view illustrating a structure of an organiclight emitting diode display according to a fourth application exampleof the present disclosure. FIG. 13 is a cross sectional viewillustrating a structure of the organic light emitting diode displayalong to the cutting line of III-III′ in FIG. 12 according to a fourthapplication example of the present disclosure. Here, as the explanationfor the thin film transistor substrate having a driver therein issimilar, a detailed explanation about the thin film transistor substrateand the organic light emitting diode will be omitted.

The plane structure of the organic light emitting diode displayaccording to the fourth application example will be explained in detailwith reference to FIG. 12. An organic light emitting diode displayaccording to the fourth application example comprises a substrate SUBincluding a display area AA for representing the video information and anon-display area NA having various elements for driving the elements inthe display area AA. In the display area AA, a plurality of pixel areasPA disposed in a matrix manner are defined. In FIG. 12, the pixel areaPA is illustrated as the dotted line.

For example, the pixel areas PA can be defined as an N (row)×M (column)matrix. However, the disposed pattern is not restricted this manner, buthas various types. Each of the pixel area PA has the same size or adifferent size. With one unit pixel having three sub pixels includingred (R), green (G) and blue (B) sub pixels, the unit pixels areregularly disposed. Explaining with a simple structure, the pixel areaPA can be defined by the crossing structure of a plurality of gate linesGL running in a horizontal direction and a plurality of data lines DLrunning in a vertical direction.

In the non-display area NA defined as the peripheral area surroundingthe pixel area PA, a data driving integrated circuit DIC for supplyingthe video data to the data line DL and a gate driving integrated circuitGIP for supplying the scan signal to the gate line GL are disposed. Fora case of a higher resolution display panel than a VGA panel in whichmore data lines DL and more driving current lines VDD may be used, thedata driving integrated circuit DIC may be externally installed from thesubstrate SUB, and data contact pads may be disposed on the substrateSUB instead of the data driving integrated circuit DIC.

In order to simply show the structure of the display, the gate drivingintegrated circuit GIP is formed on one side portion of the substrateSUB directly. The ground line VSS for supplying the ground voltage maybe disposed at the outermost side of the substrate SUB. The ground lineVSS is disposed to receive the ground voltage from an external devicelocated out of the substrate SUB, and to supply the ground voltage tothe data driving integrated circuit DIC and the gate driving integratedcircuit GIP. For example, the ground line VSS may be linked to the datadriving integrated circuit DIC disposed at the upper side of thesubstrate SUB and to the gate driving integrated circuit GIP disposed atthe right side and/or left side of the substrate SUB to surround thesubstrate SUB.

At each pixel area PA, the main elements such as an organic lightemitting diode and thin film transistors for driving the organic lightemitting diode are disposed. The thin film transistor is disposed at thethin film transistor area TA defined at one side of the pixel area PA.The organic light emitting diode includes an anode electrode ANO, acathode electrode CAT and an organic light emission layer OL insertedbetween these two electrodes. The actual emission area is decided by thearea of the organic light emission layer OL overlapping the anodeelectrode ANO.

The anode electrode ANO has a shape as to occupy some area of the pixelarea PA and is connected to the thin film transistor formed in the thinfilm transistor area TA. The organic light emission layer OL isdeposited on the anode electrode ANO. The cathode electrode CAT isdeposited on the organic light emission layer OL to cover a wholesurface of the display area AA having the pixel areas PA.

The cathode electrode CAT may go over the gate driving integratedcircuit GIP and contact the ground line VSS disposed at the outer side.So, the ground voltage can be supplied to the cathode electrode CATthrough the ground line VSS. The cathode electrode CAT receives theground voltage and the anode electrode ANO receives the voltagecorresponding to the video data and then, by the voltage differencebetween the cathode electrode CAT and the anode electrode ANO, theorganic light emission layer OL radiates the light to represent thevideo information.

The cross-sectional structure of the organic light emitting diodedisplay according to the fourth application example will be explained indetail with reference to FIG. 13. On the substrate SUB, a non-displayarea NA and a display area AA are defined. The non-display area NAincludes an area where the gate driving integrated circuit GIP and theground line VSS are disposed. The display area AA includes an area wherea switching thin film transistor ST, a driving thin film transistor DTand an organic light emitting diode OLE are defined.

The gate driving integrated circuit GIP has thin film transistors whichare formed when the switching thin film transistor ST and the drivingthin film transistor DT are formed. The switching thin film transistorST in the pixel area PA has a gate electrode SG, a gate insulating layerGI, a channel layer SA, a source electrode SS and a drain electrode SD.In addition, the driving thin film transistor DT has a gate electrode DGconnected to the drain electrode SD of the switching thin filmtransistor ST, the gate insulating layer GI, a channel layer DA, asource electrode DS and a drain electrode DD.

On the thin film transistors ST and DT, a passivation layer PAS and aplanar layer PL are sequentially deposited. On the planar layer PL, ananode electrode ANO having an isolation shape within the pixel area PAis disposed. The anode electrode ANO connects to the drain electrode DDof the driving thin film transistor DT through the contact holepenetrating the passivation layer PAS and the planar layer PL.

On the substrate SUB having the anode electrode ANO, a bank BA isdeposited for defining the emission area. By patterning the bank BA, themost center portions of the anode electrode ANO are exposed. On theexposed anode electrode ANO, an organic light emission layer OL isdeposited. Depositing a transparent conductive material on the bank BAand the organic light emission layer OL, the cathode electrode CAT isstacked. The organic light emitting diode OLED including the anodeelectrode ANO, the organic light emission layer OL and the cathodeelectrode CAT is disposed.

In the case that the organic light emission layer OL may generate thewhite lights, color filters CF may be further included for representingfull color video information. In that case, the organic light emissionlayer OL would be preferably deposited as covering the whole surface ofthe display area AA.

The cathode electrode CAT is expanded over the gate driving integratedcircuit GIP so that it may cover the display area AA and the non-displayarea NA and contact the ground line VSS disposed at the outercircumstance of the substrate SUB. As a result, the ground (or,reference) voltage can be supplied to the cathode electrode CAT via theground line VSS.

In addition, the ground line VSS may be formed at the same layer andmade of the same material with the gate electrodes SG and DG. In thatcase, the cathode electrode CAT can be connected to the ground line VSSthrough the contact hole penetrating the passivation layer PAS and thegate insulating layer GI over the ground line VSS. Otherwise, the groundline VSS may be formed at the same layer and made of the same materialwith the source-drain electrodes SS-SD and DS-DD. In this case, thecathode electrode CAT can be connected to the ground line VSS throughthe contact hole penetrating the passivation layer PAS over the groundline VSS.

In FIGS. 12 and 13, the switching thin film transistor ST and thedriving thin film transistor DT of the organic light emitting diodedisplay of the fourth application example are shown. The first and/orthe second thin film transistors T1 and/or T2, explained in the first tosecond embodiments of the present disclosure, can be applied to thesethin film transistors. For example, the second thin film transistor T2having the oxide semiconductor material can be applied for the switchingthin film transistor ST. The first thin film transistor T1 having thepolycrystalline semiconductor material may be applied for the drivingthin film transistor DT. Further, for the gate driver IC GIP, the firstthin film transistor T1 having the polycrystalline semiconductormaterial may be applied. For example, for the gate driver IC GIP, theC-MOS type thin film transistor may include P-MOS type and N-MOS typethin film transistors.

A thin film transistor substrate for a flat panel display and a displayusing the same according to the present disclosure comprises twodifferent types of thin film transistors on the same substrate so thatthe disadvantage of any one type of thin film transistor can becompensated by the other type of thin film transistor. For example, witha thin film transistor having low frequency driving characteristics, thedisplay can have the low power consumption property, and the display canbe applied to the portable and/or wearable appliances.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the spirit or scope of the invention. Thus, it isintended that embodiments of the present invention cover themodifications and variations of this invention provided they come withinthe scope of the appended claims and their equivalents.

What is claimed is:
 1. A thin film transistor substrate, comprising: asubstrate; a first thin film transistor disposed on the substrate, thefirst thin film transistor comprising: a polycrystalline semiconductorlayer; a first gate electrode over the polycrystalline semiconductorlayer; a first source electrode; and a first drain electrode; a secondthin film transistor disposed on the substrate, the second thin filmtransistor comprising: a second gate electrode; an oxide semiconductorlayer on the second gate electrode; a second source electrode; and asecond drain electrode; an intermediate insulating layer comprising anitride layer and disposed on the first gate electrode; and an oxidelayer covering the second gate electrode and disposed on theintermediate insulating layer, wherein the oxide semiconductor layer isdisposed on the oxide layer and overlaps the second gate electrode,wherein the first source electrode, the first drain electrode, and thesecond gate electrode are disposed between the intermediate insulatinglayer and the oxide layer, and wherein the second source electrode andthe second drain electrode are disposed on the oxide semiconductorlayer.
 2. The thin film transistor substrate of claim 1, furthercomprising: a gate insulating layer covering the polycrystallinesemiconductor layer, wherein the first gate electrode is disposed on thegate insulating layer and overlaps the polycrystalline semiconductorlayer.
 3. The thin film transistor substrate of claim 2, wherein: thefirst source electrode is connected to one portion of thepolycrystalline semiconductor layer through a source contact holepenetrating the intermediate insulating layer and the gate insulatinglayer; the first drain electrode is connected to another portion of thepolycrystalline semiconductor layer through a drain contact holepenetrating the intermediate insulating layer and the gate insulatinglayer; the second source electrode contacts one portion of the oxidesemiconductor layer; and the second drain electrode contacts anotherportion of the oxide semiconductor layer.
 4. The thin film transistorsubstrate of claim 3, wherein the first source electrode and the firstdrain electrode comprise a same material as the second gate electrode.5. The thin film transistor substrate of claim 4, wherein the secondgate electrode is connected to a gate line comprising the same materialas the first gate electrode, through a gate contact hole penetrating theintermediate insulating layer.
 6. The thin film transistor substrate ofclaim 4, wherein the second source electrode is connected to a data linecomprising the same material as the second gate electrode, through adata contact hole.
 7. The thin film transistor substrate of claim 1,wherein the intermediate insulating layer further comprises a loweroxide layer.
 8. The thin film transistor substrate of claim 7, whereinthe nitride layer is disposed on the lower oxide layer.
 9. A thin filmtransistor substrate, comprising: a substrate; a first semiconductorlayer disposed on the substrate, the first semiconductor layercomprising a polycrystalline semiconductor material; a gate insulatinglayer covering the first semiconductor layer; a first gate electrodedisposed on the gate insulating layer, the first gate electrodeoverlapping the first semiconductor layer; an intermediate insulatinglayer comprising a nitride layer, the intermediate insulating layercovering the first gate electrode; a second gate electrode, a firstsource electrode, and a first drain electrode disposed on theintermediate insulating layer; an oxide layer covering: the first sourceelectrode; the first drain electrode; and the second gate electrode; asecond semiconductor layer comprising an oxide semiconductor materialdisposed on the oxide layer, the second semiconductor layer overlappingthe second gate electrode; and a second source electrode and a seconddrain electrode disposed on the second semiconductor layer.
 10. The thinfilm transistor substrate of claim 9, wherein: the first sourceelectrode is connected to one portion of the first semiconductor layerthrough a source contact hole penetrating the intermediate insulatinglayer and the gate insulating layer; the first drain electrode isconnected to another portion of the first semiconductor layer through adrain contact hole penetrating the intermediate insulating layer and thegate insulating layer; the second source electrode contacts one portionof the second semiconductor layer; and the second drain electrodecontacts another portion of the second semiconductor layer.
 11. The thinfilm transistor substrate of claim 10, wherein the first sourceelectrode and the first drain electrode comprise a same material as thesecond gate electrode.
 12. The thin film transistor substrate of claim11, wherein the second gate electrode is connected to a gate linecomprising the same material as the first gate electrode, through a gatecontact hole penetrating the intermediate insulating layer.
 13. The thinfilm transistor substrate of claim 11, wherein the second sourceelectrode is connected to a data line comprising the same material asthe second gate electrode, through a data contact hole.
 14. The thinfilm transistor substrate of claim 9, wherein the intermediateinsulating layer further comprises a lower oxide layer.
 15. The thinfilm transistor substrate of claim 14, wherein the nitride layer is onthe lower oxide layer.